1. Technical Field
The present disclosure relates to an in-vehicle network system in which a plurality of electronic control units are mounted on a vehicle and mutually connected via a network in a manner enabling data communication thereamong.
2. Related Art
An in-vehicle network system is known, as disclosed in JP-A-2001-251329, for example, in which a plurality of electronic control units (ECUs) are provided on a vehicle and mutually communicably connected via a network so that data can be communicated among the ECUs. In such an in-vehicle network system, a single dominant master ECU among the plurality of ECUs transmits, via the network, information indicative of a global time, which is a reference time of the network system, to node ECUs which are slaves to the master ECU. Then, each of the node ECUs sets time by overwriting information indicative of its unique local time with the received global time information. Thus, the actions of the plurality of ECUs can be synchronized.
Further, another network system has been known, as disclosed in U.S. Pat. No. 7,200,766, for example, in which local time information is transmitted/received between a plurality of node ECUs to calculate a global time from the local times of the plurality of node ECUs. Thus, the actions of the plurality of ECUs can be synchronized.
Regarding the technique disclosed in JP-A-2001-251329, in the event failure occurs in the master ECU stopping transmission of the global time from the master ECU, each of the node ECUs will uniquely calculate its local time. This has created a problem that the local time will be differentiated between the node ECUs due to differences in arithmetic logic and clock frequencies between the node ECUs. Thus, as time passes by, the local time difference between the node ECUs will become larger.
Regarding the technique disclosed in U.S. Pat. No. 7,200,766, information is required to be transmitted/received between the plurality of node ECUs. Therefore, it has been a problem that the network is imposed with loads.